The present invention relates to measurement apparatus and more particularly to a structure for measuring the thickness of a specimen using non-contact techniques.
In the manufacture of a certain class of specimens such as optical lenses and optical coating it is necessary during and at the end of the manufacturing process to determine the thickness of the optical specimen.
Typically, measurements of optical lenses and coatings are made using a mechanical micrometer during and at the end of the manufacturing process. The micrometer must be brought in contact with the optical specimen and this frequently results in damage, such as scratches to the specimen. Also, the accuracy of the measurement made by the micrometer is not ideal, being only within the range of .+-.2.5 microns.